Leptospirosis is a world-wide zoonosis caused by infection with any of the many pathogenic serovars of Leptospira. The genus of the organisms is tremendously variable and contains in excess of 250 serovars. The prevalence of individual pathogenic serovars varies in different locales, probably influenced by such factors as climate, indigenous fauna and agricultural practices. Leptospirosis affects virtually all mammalian species. Human leptospirosis also is important and occurs endemically in the tropics and as epidemics in temperate climates. However, unlike other species, humans are not important in the maintenance of the disease in nature, and human-to-human transmission is rare.
Human vaccination against leptospirosis is a goal of the research community but progress has been extremely slow. Given the fact that canine leptospirosis is an important disease and that dogs are a source of leptospirosis, many vaccines are available against the canine disease. Commercial canine leptospirosis vaccines traditionally contain inactivated antigens of serogroups Canicola and Icterohaemorrhagiae (Ictero), and have been available for more than fifty years. Recent recommendations for Europe are to continue inclusion in the vaccine of antigen of serogroups Canicola and Ictero, plus the inclusion of antigen of serogroups Grippotyphosa (Grippo) and Australis. Whereas in the USA currently four canine vaccines with antigens of four serogroups (Canicola, ictero, Grippo and Pomona) are available, in Europe a number of traditional bivalent vaccines (Canicola, Ictero) and only one trivalent vaccine (Canicola, Ictero and Grippo) are currently available.
Most commercially available leptospirosis vaccines, if not all, comprise an immunogenic cell preparation of killed Leptospira bacteria, such as for example formaline killed whole cells. These vaccines are known to be very stable at a storage temperature well below room temperature, typically between 2° C. and 8° C. However, especially given the fact that leptospirosis is endemic in the tropics, it would be an important advantage of having vaccine stability at a temperature above room temperature, since this would allow storage under ambient conditions, not needing any cooling equipment. In the past, it has been tested whether denaturating any proteins that are present in such killed whole cell vaccines (for example by applying a heat shock treatment that does not affect the leptospira antigens), since such proteins might be responsible for the de-stability of the leptospira antigens, might lead to a significant improvement of the stability. The result however was negative.